Such an optical glass fibre and curable synthetic resin composition are described in the Dutch Patent Application NL 8.401.981 which corresponds to U.S. Pat. No. 4,741,596 issued May 3, 1988 and commonly assigned herewith. The synthetic resin coating of the glass fibre, comprising a first soft layer and a second hard layer, serves to provide a glass fibre with a large strength and a low susceptibility to microbending. In this way, transmission losses caused by mechanical deformation of the glass fibre are kept low in the widest possible temperature range. The optical glass fibre may be further protected by enveloping it in additional layers of a thermoplastic synthetic resin or metal, in the form of a cladding or in the form of a tube in which the fibre can move freely. The use of a synthetic resin composition which can be cured by actinic radiation, makes it possible to envelop the glass fibre immediately after it has been formed, for example, by drawing from a preform, which drawing and coating processes can be carried out at a high rate.
In order to reduce the risk of breakage of the glass fibre in the cabling process and during arranging the cables in a telecommunications network, the aim is to manufacture glass fibres having a great tensile strength when used under dynamic circumstances. In order to improve the operational reliability of glass fibres used in telecommunications networks, the aim is to produce glass fibres whose properties depend to the smallest possible degree on varying ambient conditions, and which exhibit a very low ageing rate. If the glass fibre is constantly subjected to a mechanical load, the risk of fatigue fracture must be minimal. It has been found that the presence of water adversely affects all the said properties.
It is an object of the invention to improve optical fibres and curable synthetic resin compositions as described hereinabove, to such an extent that the coated glass fibre exhibits a greater tensile strength, a reduced risk of static fatigue fracture and a lower ageing rate, particularly in the presence of water.